1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an in-plane switching mode liquid crystal display device which improves aperture ratio together with viewing angle and color characteristics.
2. Discussion of the Related Art
Recently, a thin film transistor-liquid crystal display (TFT-LCD), mainly used for notebook computers or, requires a large sized screen. However, the TFT-LCD has a problem in that contrast ratio is varied depending on viewing angles. To solve such a problem, various LCDs, such as a twisted nematic LCD, provided with a film-compensating mode, and a multi-domain LCD have been proposed. Such proposed LCDs substantially fail to solve problems related to contrast ratio and color.
Under the circumstances, an in-plane switching mode LCD device has been proposed to obtain a wider viewing angle.
A related art in-plane switching mode LCD device will be described with reference to the accompanying drawings.
FIG. 1 is a plan view showing a unit pixel of a related art in-plane switching mode LCD device. As shown in FIG. 1, gate lines 11 and 11a and data lines 12 and 12a are formed on a substrate to divide a pixel region. Also, the gate lines 11 and 11a are formed to cross the data lines 12 and 12a. A plurality of common electrodes 14 are formed of the same material as that of the gate lines within the pixel region in a zig-zag pattern. A common line 15 is formed in parallel with the gate lines 11 and 11a and is connected with the common electrodes 14. A data electrode 13 of a zig-zag pattern is formed substantially in parallel with the common electrodes on the same plane as the data lines 12 and 12a. A thin film transistor (TFT) 19 is formed in a region where the gate lines cross the data lines.
The common line 15, the gate lines 11 and 11a, and the common electrodes 14 are formed by the same process and are flush with one another. They are formed by a photo-etching process after depositing a metal such as Al, Mo, Ta, Al alloy by sputtering.
The TFT 19 includes a gate electrode 16 formed on the substrate and extended from the gate lines 11, a source electrode 17 extended from the data lines 12, and a drain electrode 18 connected with the data electrode 13.
The aforementioned related art in-plane switching mode LCD device utilizes a storage capacitor to better sustain a voltage applied to a liquid crystal, improve display of stable gray level, and to reduce flicker and residual images.
A storage on gate (SOG) mode and a storage on common (SOC) mode also utilize the storage capacitor.
In the SOG mode, some of (n−1)th gate line among a plurality of gate lines are used as a storage capacitor of an n-th pixel. In the SOC mode, an electrode for a storage capacitor is separately formed to be connected with a common electrode.
For reference, the related art in-plane switching mode LCD device adopts the SOC mode.
In other words, the common line 15 connected with the common electrodes 14 is used as a separate storage capacitor, and the common line 15 overlaps the data electrode 13 in a different layer to form a storage capacitor.
However, the related art in-plane switching mode LCD device has several problems.
First, since the common line and the data electrode have a zig-zag pattern, strong electric field distortion occurs in a bent portion of the zig-zag pattern. For this reason, liquid crystal molecules are irregularly arranged, thereby causing disclination.
Second, although the common line is formed of the same metal as the gate lines, an aperture ratio corresponding to an area occupied by the common line within the pixel region is reduced due to the SOC mode.
Finally, since the gate lines are formed with the common line, the process should be performed so as not to generate electrical short between the gate lines and the common line if the gate lines are formed to be adjacent to the common line. In this case, it is difficult to obtain a process margin.